1. Field of the Invention
The present invention relates to axially rotatable materials handling equipment for axially moving mixtures of solid particulate and water. More particularly, the present invention relates to a heater for a sand and stone screw conveyor, log washer, or the like, which applies heat to the apparatus to prevent ice formation inside the conveyor and to thaw and remove any ice already present in the apparatus.
2. Description of the Related Art
Aggregate materials, such as sand, stone, gravel, and the like, is frequently used in the construction industries. Aggregate material may be obtained by strip mining, quarrying, dredging, or other operations. It is necessary to load aggregate materials on trucks or railway cars for transport, and to clean or separate aggregate materials from clay, soil, or other impurities. Frequently aggregate materials are loaded using screw conveyors, and may be separated and cleaned in devices known as log washers, which may have helical screws or shafts with paddles for moving the aggregate material. Typically a screw conveyor or log washer will have an open top housing, variously referred to as a box, tank, trough, tub, or stockade, with the screws being rotatably mounted in bearings in the end walls of the housing. The housing is often mounted on an incline. A problem which develops during the winter months is that water enters the open top of the housing, either from rainfall or other environmental conditions, or in the case of log washers, by being intentionally introduced as part of the process of separating and cleaning the aggregate materials, and during the winter months, the water will freeze and form ice.
When this occurs, the equipment must be stopped and the frozen water must be warmed up to thaw and be removed. Often this happens during the winter and at night, when the temperatures are at their lowest. Then, the thawing can take place simply by waiting until daylight so that heat radiated from the sun thaws the equipment. In this case, the equipment can only be used during the daylight hours.
Alternatively, hot water can be poured into the equipment to melt the ice. Another alternative is to apply heat to the outside surface of the conveyor housing using wood fires or other combustible material, or manually applied heating devices. This alternative is time-consuming and labor-intensive.
Thus, there is a need to prevent the occurrence of frozen water in the housing of axially rotatable materials handling equipment that handles mixtures of solid particulate materials and water, thereby avoiding the need to stop the equipment to thaw it.
U.S. Pat. No. 1,609,652 issued to McQueen on Dec. 7, 1926 teaches a horizontally oriented log washer.
U.S. Pat. Nos. 1,695,021 issued to Puryear on Dec. 11, 1928, and U.S. Pat. No. 2,025,841 issued to Young on Dec. 31, 1935, teach inclined twin-screw apparatus for separating solids.
U.S. Pat. No. 2,336,991 issued to Leveke on Dec. 14, 1943 teaches a single screw gravel separator.
U.S. Pat. No. 3,674,401 issued to Annis, Jr., et al. on Jul. 4, 1972 teaches a heated injection molding apparatus including an axially rotatable conveyor screw.
U.S. Pat. No. 3,807,558 issued to Hamm on Apr. 30, 1974 teaches a sand screw and log washer.
U.S. Pat. No. 4,575,010 issued to Zimmerman on Mar. 11, 1986 teaches an apparatus for spreading heated sand onto icy roadways using a set of heaters, including a wraparound heater and an axially rotatable helix. This reference is directed to an apparatus that only contains sand that is heated, whereas the inventive apparatus handles a mixture of particulate solids and water. Note that in the application of the apparatus of Zimmerman, the weather conditions are necessarily quite cold, since the road surface being treated is frozen and the sand is intended to partially melt and embed into the ice, therefore, a mixture of particulate solids and water inside the structure during its use would defeat its purpose. The present invention also differs from the patent in the removal of thawed or melted water, which is not provided for in the apparatus of the patent.
U.S. Pat. No. 5,593,707 issued to Goe et al. on Jan. 14, 1997 teaches a heated auger conveyor for feeding polymer powder to a compacting press.
U.S. Pat. No. 6,170,667 issued to Bilak et al. on Jan. 9, 2001 teaches a multi-stage screw apparatus for preparing slurries.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a sand and stone screw heater for heating the housing of a screw conveyor or log washer for solving the aforementioned problems is desired.
The invention is directed to an axially rotatable materials handling apparatus for handling mixtures of solid particulate and water, such as a screw conveyor, log washer, or the like, in which the apparatus includes a heater mounted thereon. The preferred solid particulate material conveyed, separated, or washed in the apparatus is sand and/or stone. Solids particulate materials can be continuously added to the apparatus and be conveyed continuously to the outlet by virtue of the rotation of the axially rotatable member.
During use of the apparatus outdoors in cold weather, e.g., during the winter season, water is present in the apparatus either because it is added intentionally for washing the solid particulate or because it accumulates due to atmospheric humidity or from precipitation (e.g., snow). When the surroundings temperature falls below freezing, the water present inside the apparatus often freezes in place, thereby freezing the rotating member(s) in the apparatus.
One type of heater that can be used is a burner that burns combustible fuel, such as fuel oil or natural gas. The hot combustion gases flow from the heater through a duct (conduit) that is mounted on the housing containing the axially rotatable member and the mixture being handled. Heat is transferred from the hot combustion gases in the duct to the mixture inside the housing to thaw and melt any water present.
The duct can be applied along the entire length of the housing. Also, it can be wrapped around the bottom and sides of the housing to ensure efficient heat transfer to the mixture inside.
Alternatively, the heater can be an electric resistance heater mounted onto the housing.
Accordingly, it is a principal object of the invention to provide an axially rotatable materials handling apparatus for handling a mixture of solid particulate with water, with a heater that can be actuated as needed to thaw any water frozen inside the structure housing or to prevent any water from freezing.
It is another object of the invention to provide the above apparatus with a heater that burns combustible fuel and includes a flue duct mounted on the housing to transfer heat from the combustion gases to the mixture inside the housing.
It is a further object of the invention to provide the above apparatus in which the heater is an electric resistance heater. mounted on the housing.
Still another object of the invention is to provide the above apparatus for use as a log washer or as a conveyor.
It is an object of the invention to provide improved elements and arrangements thereof for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.